In hub units in which an inner ring element is fixed by caulking the vehicle center side end portion of the hub, the end portion to be caulked is plastically deformed by a caulking tool in such a way as to extend radially outwardly, so that the inner ring element is fastened and fixed by the plastically deformed portion thus swaged. In this process there is a risk that the inner ring element and/or the hub may be deformed to cause a change in the dimension of a track on the inner ring element or a deformation of the shape of the track surface, which can lead to deterioration in the performance of the hub unit.
To avoid deformation of the inner ring element, there has been proposed a technique in which an annular constraining jig is attached on the radially outer portion of the inner ring to suppress deformation of the inner ring (see for example Japanese Patent Application Laid-Open No. 2000-38005).
However, the constraining jig proposed in Japanese Patent Application Laid-Open No. 2000-38005 necessitates an operation of inserting it between the inner ring element and an outer ring, and in addition, that operation needs to be performed every time for every hub unit for wheel. This takes time and effort and leads to a decrease in the work efficiency and an increase in production cost.
In the caulking process according to a prior art disclosed in U.S. Pat. No. 5,226,738, caulking operation is performed by gradually pressing a cylindrical portion to be caulked provided at the vehicle center side end of a hub using a metal mold for caulking. In the final step of the caulking operation just before completion, the metal mold strongly presses the end to be caulked of the hub in the axial direction, so that a force that tends to displace the hub radially outwardly toward the inner ring element is generated at the fitting portion of the inner ring element and the hub as a component force of the pressing force. Thus, the inner ring element receives a force in radially outward directions to deform. When such deformation is large, excessive pressure in the bearing and deformation of the track can occur, which can cause shortening of the life of the bearing, an increase in the torque or noise. In addition, there is the problem that the more securely the inner ring element and the hub are fixed together, the larger the deformation of the inner ring element toward radially outward directions will become.
An object of the present invention to minimize deformation of the inner ring element generated upon caulking as much as possible, and to provide a hub unit that does not suffer from deterioration in performance.
To achieve the above object, a hub unit for wheel according to a first aspect of the present invention comprises:
an outer ring having two bearing tracks on its inner circumferential surface;
a hub having a wheel mount flange on the axially vehicle outer end side and an end portion on the axially vehicle center side, the hub having, as a separate part or integrally on its outer circumference, a first bearing track corresponding to the axially vehicle outer end side bearing track of the outer ring;
an inner ring element fitted on the end portion side of the hub, the inner ring element having on its outer circumference a second bearing track opposed to the axially vehicle center side bearing track of the outer ring and being fixed on the end portion by plastically deforming the end portion of the hub radially outwardly; and
rolling members provided between the two bearing tracks of the outer ring and the first and second bearing tracks,
wherein the outer diameter of a plastically deforming portion of the end portion is made smaller than the diameter of the portion of the inner ring element that is fitted on the hub, the start point of the small diameter portion is arranged to be situated between the start point of a chamfered portion on the inner circumferential surface of the inner ring element and the vehicle center side end face of the inner ring element, and the end portion is plastically deformed radially outwardly to fasten and fix the inner ring element.
According to the hub unit for wheel according to the first aspect of the present invention, it is not necessary to use a constraining jig when effecting the plastically deforming process.
According to the first aspect of the present invention, it is possible to fasten and fix the inner ring element on the vehicle center side of the hub while minimizing deformation of the inner ring element as much as possible, and therefore shortening of the useful life of the bearing will not occur. In addition, the length over which the inner ring element is press-fitted on the end portion is shortened, whereby assembling is made easier.
To achieve the above object, a hub unit for wheel according to a second aspect of the present invention comprises:
an outer ring having two bearing tracks on its inner circumferential surface;
a hub having a wheel mount flange on the outer end side and an end portion on the axially vehicle center side, the hub having, as a separate part or integrally on its outer circumference, a first bearing track corresponding to the axially vehicle outer end side bearing track of the outer ring;
an inner ring element fitted on the end portion side of the hub, the inner ring element having on its outer circumference a second bearing track opposed to the axially vehicle center side bearing track of the outer ring and being fixed on the end portion by plastically deforming the end portion of the hub radially outwardly; and
rolling members provided between the two bearing tracks of the outer ring and the first and second bearing tracks,
wherein a continuous circumferential groove is provided on the inner circumferential surface of the inner ring element adjacent to a chamfered portion on the inner end portion of the inner circumferential surface.
By providing a continuous circumferential groove on the inner circumferential surface of the inner ring element adjacent to a chamfered portion of the inner ring element as per the above, when the portion to be caulked is strongly pressed in the axial direction by a metal mold in the final stage of the caulking process, a portion of the material of the hub expanding radially outwardly in the fitting portion of the inner ring element and the hub is evacuated into the circumferential groove of the inner ring element, whereby the expansion is prevented from affecting the inner ring element. As a result, it is possible to reduce the radially outward force acting on the inner ring element upon caulking and circumferential stress on the outer circumference of the inner ring element.
According to the second aspect of the present invention, not only the radially outward force acting on the inner ring element can be reduced by the above described effect, but the radially expanding material of the hub intrudes into the circumferential groove, whereby the intruding portion helps to prevent axial displacement of the inner ring element relative to the hub. In this way, it is possible to fix the inner ring element more strongly, and this is advantageous also in preventing pressure failure of the hub bearing apparatus for wheel and creeping that may occur at the fitting portion of the inner ring element on the hub.
Furthermore, in the second aspect of the present invention, since the main chamfered portion on the inner ring element is left unchanged, and the circumferential groove is formed on the inner circumferential surface of the inner ring element adjacent to the main chamfered portion, the circumferential groove is not open to the inner end face of the inner ring element. Therefore, from the early stage to the final stage of caulking, the amount of the material intruding into the groove is small, and the material of the hub including a cylindrical portion to be caulked gets into the groove when a strong axial force causes a radially outward strong force acting on the inner ring element in the final stage of caulking. Therefore, it is possible to relieve the effect of the aforementioned strong force. With such intrusion of the hub material into the circumferential groove, it is also possible to prevent axial displacement of the inner ring element relative to the hub. Furthermore, according to the second aspect of the present invention, troublesome machining such as knurling can be eliminated.
As per the above, in the hub unit for wheel according to the second aspect of the present invention, when the portion to be caulked is strongly pressed in the axial direction by a metal mold in the final stage of caulking, it is possible to evacuate the portion of the hub that expands radially outwardly, in the fitting portion of the inner ring element and the hub, into the circumferential groove provided on the inner circumferential surface of the inner ring element. Therefore it is possible to reduce the radially outward force acting on the inner ring element upon caulking and to reduce expansion and deformation of the inner ring element caused by caulking. Furthermore, it is possible to prevent axial displacement of the inner ring element relative to the hub and to prevent creeping or relative movement of inner ring element in the radial direction.